[crosspolymer]

Hi all, I posted this in the undergrad forum but have had no replies, I thought it might be more suitable to post here.

I'm reading a paper that talks about measuring "crystallinity index" of a sample of apatite (https://www.sciencedirect.com/science/article/abs/pii/001670379090230I) and it talks about measuring the "splitting of a triply degenerate antisymmetric bending vibration of orthophosphate". I am a second year undergrad and I've done a few lecture courses on spectroscopy, but how can a degenerate vibrational mode exhibit splitting in IR spectroscopy? How can the modes absorb at different wavelengths if they are degenerate?

Thanks

[sjb]

No need to crosspost - locked here for now.